Process of treating rubber and product obtained thereby



Patented Oct. 14, 1930 UNITED STATES PATENT OFICE SIDNEY M. CADWELL, 0F LEONIA, NEW JERSEY, ASS IGETOR TO THE NAUGATUCK CHEMICAL COMPANY, OF NAUGATUGK, CONNECTICUT, A CORPORATION OF CON- NEGTICUT PROCESS OF TREATING RUBBER AND PRODUCT OBTAINED THEREBY No Drawing. Original application filed March 2, 1928, Serial No. 258,670. Divided and. this application filed March 2, 1928.

This invention relates to the treatment of rubber and similar materials and to the proclucts obtained thereby. The invention is more particularly concerned With new classes of chemical compounds capable of functioning as accelerators of vulcanization.

This case is a division or" copending application Serial No. 258,670, filed of even date.

Accordingly the objects of the invention include the vulcanization or" rubber treated with the hereinafter described classes of compounds. Another object is to provide new chemical compounds, particularly useful in vulcanization, which are comparatively inexpensive and at the same time highlyetficient both from the standpoint of their behavior during the compounding of rubber as Well as in the properties Which they impart to the vulcanized product. Another object of the invention is to accelerate the action of the new chemical compounds by the addition'of base to re their action by the addition al. A further object of t ie in- ,a to provide amethod whereby the orba ticeoii' the use of ac- 't is generally known that many of ounds mployed are so powerful that Lt th the mini mil is possessed by many of the accelerators which ie property of vulcanizing rubber at iry temperatures or at temperatures u 'ell below those orchnarily employed in hot vulcanization, for example at 212 F. or

thereabouts. Illustrations of such rapid accelerators are metallic dithiocarbamates, metallic salts ofother thioacids,-mercapto thiazoles and the like. According to the present invention this seriousobjection of previ anization may be entirely overcome, the compounds: may be mixed upon the m ll with practically no danger of prevulcanization thereon, u ithout sacrificing the e they cause a prevulcanization, or burning on 1. This serious disadvantage Serial No; 258,676.

accelerating power Which is desired. Certain of the compounds forming the subject matter of the present invention may be mixed With entire safety on the mixing mills, subject to the conditions hereinafter named, Where as others may be safely mixed, observing certain precautions as to mill temperatures, etc. The invention includes combining rubber and similar vulcanizable materials with a vulcanizing combination, including a vulcanizing agent, a metallic oxide or its equivalent and a phenyl methylene bis thiol derivative of a substituted dithiocarbamate, and vulcanizing the rubber. Th'e'invention also includes the products thusbbtained. The invention also includesthe preparation of the new chemicals hereindescribed The invention further consists in-accelerating the action of the compounds by the addi- Where B and X are N and S respectively, and Y is a carbon atom in a group attached at the S of Rfii-3--,

which group is here shown as phenyl methylene. The compounds comprise phenyl methylene bis t-hiol derivatives of substituted dithiocarbamates, and possess the group 1 user. 7

i The whole compound, phenyl methylene blS dimethyl dithiocarbamate, reacts at least by the addition as rapidly with sodium hydroxide in boiling aqueous alcohol as diphenylmethyl dimethyl dithiocarbamate reacts under the same conditions. All the compounds which react with sodium hydroxide at least as rapidly as diphenylmethyl dimethyl dithiocarbamate (M. P. 905-97" O.) accelerate vulcanization, in the presence of a metallic oxide, such as zinc oxide or an equivalent metallic compound.

Zinc oxide is a good illustration of a metallic oxide which may be used. In place of zinc the following elements may be used in combined form, preferably somewhat basic and soluble in rubber; mercury preferably in the mercuric state, lead preferably in the plumbous state, cadmium, copper preferably in the cupric state, arsenic preferably in the arsenous state, manganese preferably in the manganous state. Preferably the metallic compound is of such a nature that the metallic element is available during the vulcanization process. Oxides, stearates, carbonates are among the metallic compounds which may be used.

As one illustration of the invention, 100 parts of pale crepe, 10 parts of zinc oxide, 3 parts of sulphur, and 0.2 part of phenyl methylene bis dimet-hyl dithiocarbamate may be mixed together in the customary way on a mixing mill or in any other desired manner. The rubber stock thus prepared is well vu canized in 60 minutes at 20 lbs. steam pressure. The stock may also be vulcanized at higher steam pressures than 10 lbs.

Phenyl methylene bis dimethyl dithiocarbamate (benzal bis dimethyl dithiocarbamate) is a new compound the probable formula of which is UH3 NCS.

CH2 ll nocm5 s UHi N llI S on/ One method of preparing; it is as follows:

Two volumes of alcohol are added to an approximately 33'% solution of sodium dimethyl dithiocarbamate containing substantially 143 grams of sodium dimethyl dithiocarbamate and to this mixture are then added 80.5 grams of benzal chloride. The mixture is heated to 6070 for about two hours. It is then cooled, let stand for about 2 hours for complete crystallization and filter. The product is washed with a little alcohol, diluted with two volumes of water and further washed with water. It is then dried. l 'he melting, point is 181 to 183 C.

Phenyl methylene bis dimethyl dithiocarbamate functions well nhen the cure is carried out according to any of the commercial methods, such as in steam, talc, water, etc. Other dialkyl dithiocarbamates may be used,

such as phenyl methylene bis diethyldithiocarbamate, etc., provided they satisfy the condition of hydrolysis herein set forth.

I have observed that the action of the compounds disclosed herein is accelerated by the presence of a small amount of a basic material such as sodium hydroxide trisodium phosphate, dicyandiamide, piperidine, aniline, dibcnzylamine, piperazine, hydrate, triethanol'amine. The use of the base lowers the temperature at which the accelerator funct )llS or increases its speed of functionmg 1 usually increases the tensile strength at all temperatures of vulcanization about 10%.

The base may be employed in amounts gencrall less than 1% or thereabouts.

Sin-co a basic i'na-terial accelerates the ac- L' 1. blOil or the accelerator and lowers the temnerature at which it functions, it also iniscs the speed of burning on the mixing T iereforc the greater the amount of base pr nt in the mix, the greater the danger of burning on the mixing mill and rubbers which are basic therefore accelerates the action of these compounds. Burning on the mixing mill is one form of what is herein called premature vulcanization. The latter expression also includes the burning, scorchor setting up of the stock on mills, calentubing machines, as well as any prevulc. zation which may occur or be incipient prior to the actual deliberate vulcanization operation.

On the other hand the addition of acid retards the action of the accelerator and therefore improves its resistance to burning.

For example .1 part of monochlor acetic acid added to the above stock minimizes any danger of burning on the mill, but the same time does retard the rate of vulcanization. With larger amounts of acid it is possible to retard vulcanization almost to the point where no vulcanization takes place. Other acids which I have successfully employed are sulphanilic, oxalic, picric, plies phoric, trichloracetic, para toluene sulphonyl chloride and pine tar. I have also succes ully employed substances which may form acids duringthe course of vulcanizasuch as ethyl. oxalate and zinc acetate.

i :es which are slightly acid because of the presence of carbon black or pine tar resist burning; on the mill abnormally well. The vulcanization of rubbers which are acid by nature, or contain appreciable amounts of acid or acidic ingredients, is not accelerated so well by the herein described compounds, unless the acidic properties be first removed or neutralized.

Lil-.rewise, rubber or rubber stocks which are apprcciaoly basic by nature, or contain basic materials, may display a marked, often undesirable, tendency towards prevulcanization. Such basic rubbers or stocks may be of pale crepe, 10

' an d' of dithiocarbamate stock.

iz tion occurs much more treated with acidic material to remove, to curb or to control this tendency toprevut canize. Therefore, by the use of basic material and acidic material .in suitable proportions as required, any rubber or stock may be brought to a predetermined speed of vulcanization.

Instead of adding on the mixing roll the basic materials intended to activate the con1- pounds or accelerate their action, .one may permit the basic material to diffuseinto the rubl For instance if the stock given above for vulcanization inythe air be vulcanized in air containing ammonia, the vulcanization is greatly accelerated and the surface of the stock is remarkably hard and resistant to marring. The introduction of the basic material may be made on the millby diffusion from a liquid, solution, or gas, or from adjoining rubber stock or from a fabric. v

For example a stock L containing parts parts of zinc oxide, 3 parts of sulphur and .3 part of phenyl methylene bis dimethyl dithiocarbamate, made up in theusual manner, may be sheeted to say .060

inch thickness or may be inthe form of an article. If the-sheet or article be treated with gaseous ammonia for about. 16 hours, it

.will vulcanize very much more rapidly and at a lower temperature than a stock not so treated. Instead of gaseous ammonia,-I may employ aqueous ammonia, aqueous diethylamine, aqueous aniline or dimethylamine or aniline vapor. It is believed that'thesealkaline materialsdiifuse into the rubber and accelerate the actlon .of the phenyl methylene bis diethyl dithiocarbamate.

As an example ofthe'introduction by diffusion of the basic material as well as the ntroduction compounds dismosed herein, the following illustration is given. 7 100 parts of pale crepe, 10 parts of zinc oxide, 3 parts of sulphur, 1- part of phenyl methylene bis dimethyl dithiocarbamate and .2 part! of monochlor acetic acid are mixed to form one stock which is calendered to a thickness of .010. An-' ther stock is made up of 100 parts ofpale crepe, '10 parts of'zinc oxide, 3 parts of sulphur and 4: parts of dibenzylamine. .Thls stock is mixed on the mills in the usual manner and .calenderedtoa thickness of .010". The two stocks are plied up alternately using plies of each andallowed to stand for 24 hoiirs to permit the diifusion of'the dibenzvlar iine into the phenyl methylene stock the phenyl methylene bis dimethyl into the diben'zylamine Thereafter the plied up stock is heated at 212 audit is found that vulcanquickly than it do for the individual stocks which have not been plied up. It willbe observed; that .the dibenzylamine facts it'o' .neutrali e the .monochlor acetic era-tor may nga base by diffusion of some of the;

- stood-that a-vulcanizin i m proving daints, age-i-1nprovers, and.

acid as Well as to activate the phenyl methylene bis dimethyl dithiocarbamate.

As pointed out before the presence of the monochloracetic acid; improved the resistance to burning but the procedure may be carried out without the use of the acid.

The basic material (ammonia etc.) may be introduced from the surrounding medium such as air or water to neutralize the acids and/or to activate the accelerator. For instance if .2 part of acid be added to the stock for air cure given above, and the stock be cured in air containing ammonia gas the ammonia Will not only neutralize the acid but will activate the phenyl methylene bis compound. The basic material may be introduced in any desired manner at any time prior to complete vulcanization, i. e., it may be introduced during vulcanization as a gas or vapor, or it may be applied to the stock by painting, dipping, etc, before the stock subjected to vulcanization, or the stock may be vulcanized in solution or suspension of the basic material. 7

Any of these ingredients,-base, acid and accelerator may be brought together in the form of cements, i. e., a cement containingaccelbe mixed with a cement containat the timethe cement is to be used. canize appreciably at ordinary temperatures if the base be absent. Likewise, an accelerator-containing cement. may be preserved in an unvulcanized'condition for a long period by the addition of a 'V'Jhen vulcaniza tion is desired,=a base may be added (as such,

The accelerator cement will not vulidic material (as such,.in solution, orin a cement).

in solution, orin a cement) and vulcanization V will then takeplace.

The compounds in general may be used in ties. Theclaims are therefore to be broadly,

interpreted as including such treatment of rubber in any form (solid, solution dispersion) for these purposes well as for Vulcanization, in which latterinst-ance, it is underagent and a metallic oxide or its equivalent will be added to the rubber a d an antioxidant or other material the physical properties of therubher maybe present if desued. t of course understood thatnot all of these compounds of equal accelerating strength, pound for pound, under identical vulcanizing' conditionsj These accelerators maybe used in conjunction with any of the known antioxiother materials ing troduced into rubber to improve ageing and other physical properties.

It is believed that, in general, as the molecular weight of the groups attached to the nitrogen is increased the higher is the vulcanizing temperature, when equi-molecular amounts of accelerator are considered, and the more resistant are the com 'iounds to prevulcanization on the iniz-iing mills, and the better their action with litharge in the absence or nesence of zinc oxide.

The rate of reaction of the compound with sodium hydroxide in boiling aqueous alcohol may be determined as tollows:

.00125 moles of the compound is weighed into a 50 cc. Erlenmeyer; 25 cc. alcohol and .00125 moles sodium hydroxide in the form of an approximately normal solution are added and the solution brought to the boiling point as quickly as possible and kept there for exactly 30 minutes. The solution is then cooled quickly and titrated with approximately N/lO acid, using phenolphthalein as the indicator. Carbon dioxide-tree water should be used throughout. A blank should be run in order to check up on the amount of acid necessary to neutralize the sodium hydroxide when no compound is The decrease in hydroxyl ion content during the boiling is taken as a measure of the extent of the reaction with sodium hydroxide.

The above procedure constitutes a method whereby the relative rate of hydrolysis of any given compound of the types disclosed may methyl dimethyl dithiocarbamate.

The diphenylmethyl dimethyl dithiocarbamate may be prepared in accordance with the general procedure indicated herein for the related esters ot dithiocarbamates, that is, reacting in dilute alcoholic solution under heat the sodium salt,sodium dimethyl dithiocarbamate and the chloride of the ester group,-diphenyl chloro methane. The separated oil solidifies on standing and may be purified by recrystallization from alcohol in the usual manner.

It is known that the rate of hydrolysis of organic compounds, or more exactly, their rate of reaction with a base such as sodium hydroxide, varies with the substituents in the organic compound. This variation has been utilized in the present invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A. rubber product derived from rubber combined with a metallic oxide, a vulcanizing agent and a phenyl methylene bis ester of an allryl dithiocarba nic acid, which ester is capable oi": hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

2. A vulcanized rubber product derived be compared with that of diphenyl- ,voa

from rubber combined with zinc oxide, sulphur and a phenyl methylene bis dialkyl dithiocarbamate.

3. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and a phenyl methylene bis disubstitut-ed dithiocarbamate.

4. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and a phenyl methylene bis aliphatic substituted dithiocarbamate.

5. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and phenyl methylene his dimethyl dithiocarbamate.

6. A method of treating rubber which comprises vulcanizing rubber containing a metallic oxide and a vulcanizing agent in the presence of a phenyl methylene bis compound of substituted dithiocarbamate, which compound is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

7. A method of treating rubber which comprises vulcanizing rubber containing a metallic oxide and a vulcanizing agent in the presence of a phenyl methylene bis compound of a disubstituted dithiocarbamate, which compound is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

8. A method of treating rubber which comprises vulcanizing rubber containing a metallic oxide and a vulcanizing agent in the presence of a phenyl methylene bis compound of an aliphatic substituted dithiocarbamate, which compound is capable or hydrolyzing in aqueous alcohol. in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

9. A met 10d of treating rubber which comprises vulcanizing rubber containing zinc oxide and sulphur in the presence of a phenyl methylene bis compound of an allryl dithiocarbamate, which compound is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

10. A. method of treating rubber which comprises vulcanizing rubber containing Zinc oxide and sulphur in the presence of a phenyl methylene bis compound of a disubstituted dithiocarbamate, which compound is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

11. A method of treating rubber which comprises vulcanizing rubber containing zine oxide and sulphur in the presence of a phenyl comprises vulcanizing rubber containing Zinc oxide and sulphur in the presence of phenyl methylene bis dimethyl dithiocarbamate.

Signed at New York, county and State of New York, this 23rd day of February, 1928.

SIDNEY M. OADWELL. 

